1. Field of the Invention
This invention relates to a PF-LCD (polymer film liquid crystal display device) which is a liquid crystal display device using substrates implemented by polymer films, and which particularly delimits a film composition and thickness of upper and lower polarizing plates and/or a thickness of a cohesive agent so as to improve irregularities of colors of the PF-LCD.
2. Discussion of the Background
FIG. 1 shows a background art apparatus of a PF-LCD. In this device in FIG. 1, two polymer film substrates 10 are provided. Further, a lower polarizing plate 16 is formed on a lower surface of a lower of the polymer film substrates 10. A reflective plate 19 is formed adjacent to the lower polarizing plate 16, on an opposite face as the shown lower polymer film substrate 10. An alignment layer 15 which includes transparent electrodes 17 is formed on a surface of the lower shown polymer film substrate 10. A central portion of the PF-LCD device includes a liquid crystal layer 13 and spacers 18. Formed above the upper shown polymer film substrate 10 is a phase plate 12 and then an upper polarizing plate 14.
A concern with such a PF-LCD device as shown in FIG. 1 is that a thickness of the liquid crystal layer 13 must be maintained to be even. If liquid crystal layer 13 is not maintained to have an even thickness, irregularities in color result from any unevenness in the thickness of the liquid crystal layer 13.
The device as shown in FIG. 1 utilizes polymer films for the substrates 10, and also particularly for the upper polarizing plate 14 and lower polarizing plate 16, to assure an ultra-thin and light weight design. However, the use of such polymer films for the upper polarizing plate 14 and the lower polarizing plate 16 results in such an upper polarizing plate 14 and lower polarizing plate 16 being somewhat flexible, in comparison with a device which may utilize a rigid glass structure. The utilization of polymer films for the upper polarizing plate 14 and lower polarizing plate 16 provides the benefits of the device of FIG. 1 being ultra-thin and light weight, but provides the drawbacks that variations in a liquid crystal layer 13 are more apt to occur, i.e., a thickness of the liquid crystal layer 13 may not be as uniform as desired.
One manner in addressing this issue, as disclosed in Japanese patent publication no. 06-67172, by the Applicants of the present application, is to include at least one layer of plastic film as a reinforcing plate at an outer layer of the PF-LCD panel to reduce any deformation of the panel, and thereby to reduce any nonuniformity of the liquid crystal layer 13. Such a deformation of the panel may be particularly appreciable from changes in temperature and humidity.